In a process of attaching multiple, tiny, discrete electrical devices or integrated circuit chips to a plastic circuit board (PCB), a pick-and-place machine can be used to pick up a part from a tray, rotate the part to a particular angular orientation, and then accurately place the part on a PCB. A typical machine placement accuracy should be about 0.006 inches (6 mils).
The consequence of inaccurate placement on the PCB is that a misalignment of the part lead over a solder bonding area can result in poor or lack of electrical contact between the part lead and the PCB conductor. The bonding is accomplished by inserting the loaded PCB in a furnace to melt the solder paste. A typical printed circuit assembly (PCA) can consist of numerous types of parts of components attached to a PCB.
If the pick-and-place machine has a consistent or periodic error, there can be catastrophic results in manufacturing these PCA's. A typical pick-and-place machine can have one or more, i.e. 12, rotating or linear motion heads with vacuum connections for picking. The rotation of the head places parts typically at 0.degree. , 90.degree. , 180.degree. , and 270.degree. on the PCB to match PCB connections. It is important that the placement be accurate in the X-plane, Y-plane, and angular orientation.
A glass board and glass part device is currently available from Fuji Electric Company that can be used to check pick-and-place machine accuracy in placement of a "glass" quad flat pack (QFP).
There are marks on the glass that differ in distance (i.e., 0.005") between marks compared to the leads of the QFP device. Thus, a misplaced device can be located by noting which of the marks line up with a corresponding lead.
This device has limited use in that it is not using the actual part but a glass part that simulates the QFP device. It, therefore, does not include the inherent dimensional differences within the device tolerances.
It is, therefore, the purpose of this invention to provide a unique, simple, automatic, accurate apparatus that, by a gray scale camera, determines proper micro chip or discrete device placement on a PCB. This invention utilizes a glass plate similar to that described in U.S. Pat. application Ser. No. 07/783,111, filed 10/25/91, by the same inventor and having a common assignee. The apparatus provides feedback to an operator on a periodic basis identifying improper part placement.